The phase locked loop (PLL) is a building block for a wide variety of electronic devices. A PLL is a phase feedback system that includes a phase detector, a low-pass filter and a voltage-controlled oscillator (VCO) in the feedback path. When there is no reference signal to the loop the voltage-controlled oscillator operates at a free-running frequency. If a reference signal is applied, usually by a crystal controlled oscillator, the phase detector compares the phase and frequency of the input reference with the signal of the VCO, of signal produced therefrom by division, and generates an error voltage that is related to the difference in the two signals. The error voltage is then filtered and applied to the control of the VCO thereby varying the VCO frequency in a direction that reduces the frequency difference between the two signals. When the frequencies of the two signals become sufficiently dose, the negative feedback nature of the system causes the system to lock with the incoming signal. Once in lock, the VCO frequency and phase is aligned with the frequency of the reference signal, except for a finite phase difference which is necessary to generate the corrective error voltage to shift the VCO frequency to the input signal frequency, thus keeping the system in lock.